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Improved examples for offset(), and slight docs tweak.

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Adrian Mariano 2019-07-16 16:51:53 -04:00
parent 9c4ef743c2
commit a89c324b4c
1 changed files with 29 additions and 10 deletions
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geometry.scad
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@ -810,8 +810,8 @@ function _offset_region(
// Function: offset()
//
// Description:
// Takes an input path and returns a path offset by the specified amount. As with offset(), you can use
// r to specify rounded offset and delta to specify offset with corners. Positive offsets shift the path
// Takes an input path and returns a path offset by the specified amount. As with the built-in offset() module, you can use
// `r` to specify rounded offset and `delta` to specify offset with corners. Positive offsets shift the path
// to the left (relative to the direction of the path).
//
// When offsets shrink the path, segments cross and become invalid. By default `offset()` checks for this situation.
@ -841,10 +841,6 @@ function _offset_region(
// firstface_index = starting index for face list. Default: 0.
// flip_faces = flip face direction. Default: false
// Example(2D):
// test = [[0,0],[10,0],[10,7],[0,7], [-1,-3]];
// polygon(offset(test,r=1.9, closed=true, check_valid=true,quality=2));
// %down(.1)polygon(test);
// Example(2D):
// star = star(5, r=100, ir=30);
// #stroke(closed=true, star);
// stroke(closed=true, offset(star, delta=-10, closed=true));
@ -868,10 +864,33 @@ function _offset_region(
// star = star(5, r=100, ir=30);
// #stroke(closed=true, star);
// stroke(closed=true, offset(star, r=10, closed=true));
// Example(2D):
// ellipse = scale([1,0.3,1], p=circle(r=100));
// #stroke(closed=true, ellipse);
// stroke(closed=true, offset(ellipse, r=-15, check_valid=true, closed=true));
// Example(2D): This case needs `quality=2` for success
// test = [[0,0],[10,0],[10,7],[0,7], [-1,-3]];
// polygon(offset(test,r=1.9, closed=true, quality=2));
// //polygon(offset(test,r=1.9, closed=true, quality=1)); // Fails with erroneous 180 deg path error
// %down(.1)polygon(test);
// Example(2D): This case fails if `check_valid=true` when delta is large enough because segments are too close to the opposite side of the curve.
// star = star(5, r=22, ir=13);
// stroke(star,width=.1,closed=true);
// color("green")
// stroke(offset(star, delta=9, closed=true),width=.1,closed=true); // Works with check_valid=true (the default)
// color("red")
// stroke(offset(star, delta=10, closed=true, check_valid=false), // Fails if check_valid=true
// width=.1,closed=true);
// Example(2D): But if you use rounding with offset then you need `check_valid=true` when `r` is big enough. It works without the validity check as long as the offset shape retains a some of the straight edges at the star tip, but once the shape shrinks smaller than that, it fails. There is no simple way to get a correct result for the case with `r=10`, because as in the previous example, it will fail if you turn on validity checks.
// star = star(5, r=22, ir=13);
// color("green")
// stroke(offset(star, r=8, closed=true,check_valid=false), width=.1, closed=true);
// color("red")
// stroke(offset(star, r=10, closed=true,check_valid=false), width=.1, closed=true);
// Example(2D): The extra triangles in this example show that the validity check cannot be skipped
// ellipse = scale([20,4], p=circle(r=1));
// stroke(ellipse, closed=true, width=0.3);
// stroke(offset(ellipse, r=-3, check_valid=false, closed=true), width=0.3, closed=true);
// Example(2D): The triangles are removed by the validity check
// ellipse = scale([20,4], p=circle(r=1));
// stroke(ellipse, closed=true, width=0.3);
// stroke(offset(ellipse, r=-3, check_valid=true, closed=true), width=0.3, closed=true);
// Example(2D):
// sinpath = 2*[for(theta=[-180:5:180]) [theta/4,45*sin(theta)]];
// #stroke(sinpath);